The present invention is related to cartridges comprising a support for attachment of (a) semi-permeable membrane(s) thereto, in which the support comprises an integrated permeate collection channel.
Membrane cartridges of the above kind are known from e.g. WO 2013/113928, WO 2006/091157, EP 0662341, and EP 1366804. These cartridges comprise a rigid planar support structure and one or more filtration layers, usually made of an organic semi-permeable membrane, provided on at least one side and typically on both sides of the support structure. The support structure typically comprises integrated permeate collection channels formed within the structure, between the opposite external surfaces onto which the membrane layers are provided. The integrated permeate collection channels are connected to an outlet port of the cartridge for evacuating permeate (e.g., the filtrate).
The membrane cartridges are e.g. used in filtration modules, in which a large number of cartridges are stacked. Typically, such as in wastewater purification and bioreactors, the filtration modules are completely submerged in the waste water. Air bubbling is provided underneath the stack of filtration cartridges in order to create an upward flow of waste water along the membranes. The air bubbles are also effective in scrubbing the membrane surface thereby removing solids which would tend to adhere to the membrane. Filtration modules of the above kind are described in e.g. WO 03/037489 and EP 0662341.
It has been observed that air bubbling is of critical importance for a correct functioning of the filtration module. It should be ensured that air bubbling is applied as uniformly as possible along all the membrane surfaces of each cartridge, so that each cartridge within the module can function optimally. It is to be further noted that aeration counts for a significant part of the operational cost of filtration apparatuses.
In addition, there is a tendency towards constructing larger bioreactors and filtration apparatuses, and in these large systems it is key to make optimal use of the available volume. Therefore there is a tendency towards increasing the membrane (filtration) surface area per unit volume as much as possible. In this regard, the aerators used underneath the stacks of filtration cartridges take up a fairly large volume which cannot be used for filtration.